Added ArrayString::from constructor that takes string slice.

Also added corresponding test.

tests/tests.rs

@@ -25,17 +25,6 @@ fn test_simple() {
     assert_eq!(sum_len, 8);
 }
 
-#[test]
-fn test_u16_index() {
-    const N: usize = 4096;
-    let mut vec: ArrayVec<[_; N]> = ArrayVec::new();
-    for _ in 0..N {
-        assert!(vec.push(1u8).is_none());
-    }
-    assert!(vec.push(0).is_some());
-    assert_eq!(vec.len(), N);
-}
-
 #[test]
 fn test_iter() {
     let mut iter = ArrayVec::from([1, 2, 3]).into_iter();
@@ -288,7 +277,6 @@ fn test_string() {
     let tmut: &mut str = &mut t;
     assert_eq!(tmut, "ab");
 
-
     // Test Error trait / try
     let t = || -> Result<(), Box<Error>> {
         let mut t = ArrayString::<[_; 2]>::new();
@@ -296,4 +284,9 @@ fn test_string() {
         Ok(())
     }();
     assert!(t.is_err());
+	
+	// Test `from` constructor
+    let u = ArrayString::<[_; 11]>::from(text).unwrap();
+	assert_eq!(&u, text);
+    assert_eq!(u.len(), text.len());
 }